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                            <div style="color:gray; word-break: break-all; font-size:12px;">原英文版地址: <a href="https://www.elastic.co/guide/en/elasticsearch/reference/7.7/rank-feature.html" rel="nofollow" target="_blank">https://www.elastic.co/guide/en/elasticsearch/reference/7.7/rank-feature.html</a>, 原文档版权归 www.elastic.co 所有<br/>本地英文版地址: <a href="../en/rank-feature.html" rel="nofollow" target="_blank">../en/rank-feature.html</a></div>
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<a id="rank-feature"></a>rank_feature(特征排名)数据类型
</h2>
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<p><code class="literal">rank_feature</code>字段可以对数字进行索引，以便以后可以使用它们来提升<a class="xref" href="query-dsl-rank-feature-query.html" title="排名特性查询"><code class="literal">rank_feature</code></a>查询中的文档的相关性评分。</p>
<div class="pre_wrapper lang-console">
<pre class="programlisting prettyprint lang-console">PUT my_index
{
  "mappings": {
    "properties": {
      "pagerank": {
        "type": "rank_feature" <a id="CO320-1"></a><i class="conum" data-value="1"></i>
      },
      "url_length": {
        "type": "rank_feature",
        "positive_score_impact": false <a id="CO320-2"></a><i class="conum" data-value="2"></i>
      }
    }
  }
}

PUT my_index/_doc/1
{
  "pagerank": 8,
  "url_length": 22
}

GET my_index/_search
{
  "query": {
    "rank_feature": {
      "field": "pagerank"
    }
  }
}</pre>
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<div class="console_widget" data-snippet="snippets/696.console"></div>
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<table border="0" summary="Callout list">
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO320-1"><i class="conum" data-value="1"></i></a></p>
</td>
<td align="left" valign="top">
<p>特征排名字段必须使用<code class="literal">rank_feature</code>字段类型</p>
</td>
</tr>
<tr>
<td align="left" valign="top" width="5%">
<p><a href="#CO320-2"><i class="conum" data-value="2"></i></a></p>
</td>
<td align="left" valign="top">
<p>与分数负相关的等级特性需要声明它</p>
</td>
</tr>
</table>
</div>
<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p>
<code class="literal">rank_feature</code>字段仅支持单值字段和严格的正数值。

多值字段及负数值会别拒绝。
</p>
</div>
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<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p>
<code class="literal">rank_feature</code>字段不支持查询，排序和聚合。

它们只能在<a class="xref" href="query-dsl-rank-feature-query.html" title="特征排名查询"><code class="literal">rank_feature</code></a>查询内部使用。
</p>
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<div class="note admon">
<div class="icon"></div>
<div class="admon_content">
<p><code class="literal">rank_feature</code>字段仅保留9个有效位的精度，这相当于大约0.4%的相对误差。</p>
</div>
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<p>
与分数负相关的特征排名应将<code class="literal">positive_score_impact</code>设置为<code class="literal">false</code>(默认为<code class="literal">true</code>)。

<a class="xref" href="query-dsl-rank-feature-query.html" title="特征排名查询"><code class="literal">rank_feature</code></a>查询将使用它来修改评分公式，使评分随着特征值的增加而减少，而不是增加。

例如，在网络搜索中，url的长度是一个常用的特征，它与分数负相关。
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